Helicopter rotor and method of repairing same

ABSTRACT

An aerofoil, particularly a helicopter main rotor blade has a leading edge protector comprising a strip of resilient polymer, preferably polyurethane, adhered to the leading edge of the blade.

FIELD OF THE INVENTION

[0001] The present invention relates to aerofoils, and more particularlyto the protection of aerofoil leading edges from erosion damage. Theinvention has particular application to rotary wings, for examplehelicopter rotor blades.

BACKGROUND

[0002] The invention was developed in the environment of helicopterrotor blade repair, and will be described primarily in connection withthat application. It will be understood by those knowledgeable in theart that the invention may have wider application to aerofoils for otherpurposes.

[0003] The leading edges of helicopter rotor blades are subject toenvironmental wear, particularly when the helicopter is operated inharsh conditions, for example with significant quantities of ambientsand or salt. It has been found in particular that there is a recurringproblem of skin erosion located inboard of the metal leading edgeabrasion strips in main rotor blades. Current practice is to remove theblades from the helicopter and send them for repair. In some cases, thedamage cannot be repaired The damage requires skin repairs to theleading edge with reinforcement doublers applied. It has been found thata metal skin repair in the flex section of the blade is prone todelamination.

[0004] Impact damage is another significant concern with rotor bladessince impact damage to the blade also requires removal of the blade andshipping to specialized shop capable of performing the repairs.

[0005] Either repair, of erosion or impact damage can mean several weeksdowntime for the aircraft while the blade is dismounted, packed andshipped, repaired and returned.

[0006] The present invention is concerned with an alternativearrangement that ameliorates many of the problems with current repairtechniques for aerofoil leading edges.

SUMMARY

[0007] According to one aspect of the present invention there isprovided an aerofoil for use in an aircraft, the aerofoil having aleading edge and a wear resistant, resilient polymeric materialextending along at least a portion of the leading edge.

[0008] The polymeric leading edge has been found to provide goodresistance to erosion. It has been found to be particularly effective inthe flex section of helicopter main rotor blades as the flexibility ofthe material limits any tendency to delaminate as occurs with rigidmetal leading edge repairs in this section of the blade. On the otherhand, it is to be noted that when used in the outboard flight section ofa helicopter rotor, the high centrifugal forces on the polymer may causecreep of the material, leading to the polymer disengaging off the end ofthe blade. In consequence, the polymer leading edge is, in thisenvironment, preferably limited to the flex section of the blade, withthe flight section being equipped with a conventional metal leadingedge.

[0009] Minor impact damage to a polymeric leading edge can readily berepaired in the field rather than dismounting the blade and shipping itaway for repair, as would be the case with damage to a conventionalleading edge.

[0010] According to another aspect of the present invention there isprovided a method of protecting the leading edge of an aerofoil fromerosion, comprising securing to the leading edge a layer of resilientpolymeric material.

[0011] The installation of the polymeric leading edge is much moreeasily performed than the installation of a metal leading edge. Itconforms more closely to the blade configuration since the metal edge isconventionally shaped using a brake, forming a sequence of substantiallyflat segments only approximating the smooth, uniform curvature of theoriginal blade.

[0012] Where the aerofoil is a rotor blade for a rotary wing aircraftwith a mounting end for attachment to a rotor drive, a flight sectionadjacent a blade tip, opposite the mounting end and a flex sectionbetween the flight section and the mounting end, the method preferablycomprises securing the resilient polymer to the leading edge of the flexsection.

[0013] The resilient polymer is preferably an elastomeric material, forexample polyurethane. The currently preferred material is ether urethane85 Shore A polyurethane, desirably black in colour with a matte finishand UV stabilized. It is preferably bonded to the leading edge skinusing an adhesive and with a bond line thickness control medium. Thismay be a scrim cloth.

[0014] The currently preferred adhesive is an epoxy adhesive, Hysol EA9309.3NA containing 5-mil glass beads for bond line thickness control.It is preferably cured at an elevated temperature, with a uniformpressure applied over the polyurethane.

BRIEF DESCRIPTION OF THE DRAWINGS

[0015] In the accompanying drawings, which illustrate an exemplaryembodiment of the present invention:

[0016]FIG. 1 is a plan view of a helicopter rotor blade;

[0017]FIG. 2 is an exploded section along line II-II of FIG. 1; and

[0018]FIG. 3 is an exploded isometric of a leading edge repair.

DETAILED DESCRIPTION

[0019] Referring to the accompanying drawings, there is illustrated ablade 10 for use in a helicopter main rotor. The blade has a mountingend 12 carrying a mounting fitting 14 which is used to mount the bladeon the rotor hub of the aircraft. The opposite end of the blade is theblade tip 16. That section of the blade adjacent the tip is the flightsection 18 which, because it is furthest from the axis of rotation,travels at the greatest speed and provides the majority of lift. Inboardof the flight section, 18 is the flex section 20 which, in use,undergoes bending deflection under the lift forces exerted on the blade.

[0020] The entire blade has an aerofoil shape as shown most particularlyin FIG. 2.

[0021] The leading edge 22 of the blade is subject to erosion duringuse. The erosion is most pronounced in the flight section where thespeed of the blade is highest. To limit erosion in the flight section,the rotor is equipped with an erosion strip 24. When wear of the erosionstrip reaches an unacceptable level, it is removed and replaced. Withthe present invention, For leading edge wear inboard of the erosionstrip, the worn skin of the rotor is abraded and cleaned and equippedwith a polyurethane leading edge strip 26 as edge protection.

EXAMPLE

[0022] With the illustrated blade 10, the repair area of the blade ismarked off. It is then abraded and cleaned with an appropriate solvent.

[0023] The bonding surface 30 of a polyurethane strip 32 is also abradedand cleaned with a solvent.

[0024] Adhesive 34 is applied to the abraded bonding surfaces of theblade and the polyurethane strip.

[0025] A scrim cloth 36, in this case 0.008 inch (00.2 mm.)nylon ispositioned smoothly over the repair area, leaving no wrinkles orcreases.

[0026] The polyurethane strip 32 is then positioned on the repair areaover the scrim cloth and subjected to a uniform pressure of 15 psi (10⁵N/m²) and an elevated temperature (e.g. 180° F. (82° C.) for a durationsufficient to cure the adhesive. It has been found that good conformityto the original shape of the blade and uniform adhesion are achievedthrough the use of a pressurized bladder acting on the outer surface ofthe polymeric sheet during curing of the adhesive.

[0027] This produces the polyurethane leading edge protector 26 in theflex section, abutting the metal edge protection used in the flightsection at a junction 38 where the edge of the metal sheet of the flightsection edge protection 24 provides a surface against which the outboardedge of the polyurethane sheet 32 engages, to support the polyurethanesheet against creep owing to the centrifugal force that is generatedduring operation of the blade.

[0028] While one particular embodiment of the present invention has beendescribed in the foregoing, it is to be understood that otherembodiments are possible within the scope of the appended claims. Thus,while the present invention has been described in connection with itsapplication to helicopter main rotor blades, it is to be understood thatthe invention has application to other aerofoils that require edgeprotection. Examples may include the wings of fixed wing aircraft andthe leading edges of aircraft propellers. The invention is therefore tobe considered limited solely to the scope of the appended claims.

Embodiments of the invention in which an exclusive property or privilegeis claimed are defined as follows:
 1. An aerofoil for use in anaircraft, the aerofoil having a leading edge and a wear resistantpolymeric material extending along at least a portion of the leadingedge.
 2. An aerofoil according to claim 1 wherein the polymeric materialis an elastomer.
 3. An aerofoil according to claim 1 wherein thepolymeric material is polyurethane.
 4. An aerofoil according to claim 1,wherein the aerofoil is a rotor blade for a rotating wing aircraft. 5.An aerofoil according to claim 4 wherein the rotor blade has an inboardend section for attachment to a rotor drive, an outboard flight sectionadjacent an outboard tip end of the blade and a flexible blade sectionbetween the inboard and outboard sections of the blade, the polymericmaterial being applied to the leading edge of the flexible bladesection.
 6. A method of protecting the leading edge of an aerofoil fromerosion, comprising securing to the leading edge a layer of resilientpolymer material.
 7. A method according to claim 6 wherein the aerofoilis a rotor blade for a rotary wing aircraft with an inboard mounting endfor attachment to a rotor drive, a flight section adjacent an outboardblade tip opposite the mounting end and a flex section between theflight section and the mounting end, the method comprising securing theresilient polymer to the leading edge of the flex section.
 8. A methodaccording to claim 6 wherein the resilient polymer is an elastomericmaterial.
 9. A method according to claim 6, wherein the resilientpolymer is polyurethane.
 10. A method according to claim 6 comprisingapplying a bond line thickness control medium to the leading edge andapplying the resilient polymer to the thickness control medium.
 11. Amethod according to claim 10 wherein the bond line thickness controlmedium is a scrim cloth.